"Sanctions will remain in place until final, fully verified denuclearisation as agreed to by Chairman Kim (Jong Un) occurs," Pompeo said, speaking in Tokyo after talks with his Japanese and South Korean counterparts.

"While we are encouraged by the progress of these talks, progress alone does not justify the relaxation of the existing sanctions regime."

Pompeo held more than eight hours of talks with North Korean officials in Pyongyang from Friday, seeking to flesh out a bare bones deal made by US President Donald Trump and North Korea's Kim last month.

He characterised the discussions as positive, but hours after he left Pyongyang, North Korea issued an angry statement rejecting what it described as Washington's "gangster-like" demand for rapid nuclear disarmament.

Pompeo, who was in Tokyo to brief his Japanese and South Korean counterparts on the talks, brushed aside the characterisation, saying discussions were continuing in "good faith".

"If those requests were gangster-like, the world is a gangster, because there was a unanimous decision at the UN Security Council about what needs to be achieved," he said.

Pompeo also insisted that Pyongyang was committed to broad denuclearisation and said that while some security guarantees could be on the table during the process, sanctions relief would not be.

"Across the range of weapons and missiles, it's a broad definition of denuclearisation, and the North Koreans understand that and have not challenged that," he said.

"There will be a verification connected to the complete denuclearisation, it's what President Trump and Chairman Kim both agreed to," he added.

"There will be things that take place along the way that help achieve the security assurances that the North Koreans need."

"But the economic sanctions are a different kettle of fish altogether... the world will see continued enforcement actions by the United States in the days and weeks ahead."